This disclosure is directed to systems for measuring the dielectric constant of well bore fluids which provide an output indicative of the dielectric constant, and hence an indication of oil and water mixture in a well borehole. In drilling a well, formation fluids which are a mixture of oil and water are often produced. After the well has been drilled and during production, it may again produce a mixture of oil and water. This mixture may change over a period of time so that measurement of the ratio of oil and water is important to proper production of the well. In summary, an important characteristic is the ratio or mixture of oil and water. The present apparatus takes advantage of the differences in dielectric constant of the mixture of the two constituents in the well borehole fluids. Water has a dielectric constant about twenty times greater than that of oil.
The present apparatus utilizes quite high frequencies which are coupled through coaxial lines with appropriately connected terminations to thereby couple electrically the fluid into the line for obtaining transmission measurements. Substantially, the response is independent of temperature and is a response from a relatively large volume of fluid to avoid localized irregularities. It utilizes conductors of coaxial construction extending from a sonde into the fluid in one embodiment, or submerged in fluid within the sonde so that the mixture of produced oil and water from the well can be measured. It utilizes a coaxial cable, and in particular two lengths thereof, the two lengths of cable being mechanically coupled by means of an appropriately constructed window further having a coupling relationship through the window. In other words, the transmitted signal is coupled through the window into the liquid which submerges the immediate vicinity of the sonde. The output can be read at a particular terminal in the form of an output voltage. The output voltage can be converted by means of relatively linear calibrations so that the output is a correctly indicated measure of percent of oil and water in the well bore fluids. To this end, the equipment preferably utilizes a microwave generator which serves as a transmitter and appropriate lengths of coaxial cable terminating at an appropriate matched load or resistance together with a signal detection circuit.
The present apparatus can be used in a continuous wave (CW) mode so that it is able to provide a continual reading as the supportive sonde is moved along the well borehole. The output can be calibrated relative to known mixtures so that output voltages relative to the mixtures can be calibrated to read either in volts or directly in percent mixture of water and oil.